Scientist plots codling moth’s demise
Steve Garczynski has novel ideas for tackling the pest.
Dr. Steve Garczynski loves to dream, and recently landed his dream job. He’s joined the research team at the U.S. Department of Agriculture’s Yakima laboratory at Wapato, Washington, with the mission of finding novel methods for codling moth control using genetics and molecular biology.
When asked to propose specific projects he’d like to tackle in the eternal effort to outwit the codling moth, Garczynski responded with a whole list of ideas.
“Science to me is addictive,” he said. “It’s almost like a hobby. It’s not like coming to work. It’s like being a kid in a candy store, there’s so much to do.”
With a bachelor’s degree in genetics from Purdue University, and a master’s degree and doctorate in molecular entomology from the University of Georgia, he feels the job is a perfect match for his experience and interests. He did graduate work on the mode of action of the microbial pesticide Bacillus thuringiensis in Lepidoptera. “I love bacterial toxins,” he enthused.
Bt has been used successfully in transgenic cotton and corn for more than a decade, with no signs of the target pests developing resistance, he pointed out.
“It’s hitting something and killing the bugs for some reason, and they’re not able to overcome it readily.”
Garczynski said the way it kills the insect is straightforward. Bt is similar to other bacterial toxins, such as those that cause cholera or food poisoning in humans. Basically, when an insect ingests Bt, the toxin hits the midgut, and the cells of the gut slough off. The insect stops feeding and gets a big stomachache. It doesn’t know it should drink lots of fluids, so it dehydrates, keels over, and dies.
But Garczynski wants to look much deeper into the effects and find the underlying mechanisms. “I have an alternative hypothesis on how Bt toxins actually work,” he said. “I think there’s more than what people currently view the mode of action being.”
Many mammalian toxins disrupt molecules in the second messenger system (the pathway through which cells communicate), so that cells can’t transmit or receive signals from other cells. In the case of an insect that has ingested Bt, the disruption of the messenger system might result in it losing the desire to eat, so it stops feeding.
Bt has been less successful as a control for codling moth than for some other pests, and the primary reason is the lifestyle of the pest, Garczynski believes. Young codling moth larvae eat treated foliage or fruit surfaces for only a short time before they find a safe haven inside the fruit.
But if scientists knew exactly how Bt works, it might be possible to find new chemicals that directly target the codling moth’s intracellular communication system without the insect needing to digest the compounds. If such chemicals could be absorbed through the insect’s cuticle, rather than ingested, they might be more effective, and this also would help in resistance management.
After identifying potential intracellular targets in the lab, Garczynski would contact chemical companies to find out if they have chemicals that could hit those targets.
He would like also to explore the idea of disrupting the insect’s receptors that detect smell and taste, so the pest doesn’t recognize the apple odor that normally attracts it to the fruit. Or, if he can identify the receptors in male moths that pick up female pheromones, it might be possible to find chemicals that are more potent than the pheromones currently used in mating disruption and that can be used as super attractants. Perhaps there’s an attractant to which both males and females would respond.
He’d like to look more deeply into how insects go into and out of diapause in the winter. If he can identify the hormones in the codling moth that control diapause and what signaling systems the hormones regulate, it might be possible to develop biorational chemicals to disrupt the production of those hormones to either prevent the insect from going into diapause or force it into diapause.
Genetic manipulations of insects for effective biocontrol have yet to be developed. Should they become so, Garczynski has other ideas, too. For example, the insect might be modified genetically with something that disrupts the production of the diapause hormone so it goes into permanent diapause. Or, if the diapause promoter region of the gene is identified, it could be altered so that when the gene is ready to express the diapause hormone, it expresses something that kills the insect.
In any case, scientists have had little success with genetically modified insects, Garczynski said.
“They can make the transgenic insect, but how do you propagate it? How do you play God? These things are so complex, we don’t understand a lot of things that regulate how insects become resistant to different things. When you get junk DNA put in, sometimes it gets thrown back out. Sometimes the insect rejects those modifications. That’s why I think biorational pesticides are probably more realistic than thinking about genetically modified organisms.”
Even if it were possible to modify an insect and propagate it, a certain proportion of the insects would probably survive in the field, and the scientist would soon be faced with another ten years of research to modify it again, Garczynski pointed out.
Biological systems are often too complex to understand. An insect has about 14,000 genes, compared with about 23,000 in a human. Scientists have sequenced the silk moth genome, but not yet codling moth. Even if the genes are mapped, you still have to find out how they work, he said. “Until you go in and do your experiments to see where things are and how you might target them, it’s just like shooting in the dark.
“To me, it’s a big puzzle, and I love puzzles,” he added. “Everything is a puzzle. I try to view the world through the eyes of a six-year-old. If we can make things simpler, rather than making them complex, it might be easier to identify novel ways of insect control.”
Garczynski has a codling moth cell line that he can genetically modify to see how things work in the cell instead of working on the whole organism. In the future, if genetic modification becomes more acceptable, this will help scientists respond better to the public about how the modification will work and how it won’t be harmful to other organisms.
In a perfect world, scientists would be able to develop an apple tree that codling moths won’t eat, he said. Or perhaps trees that are attractive and lethal to codling moth could be planted, luring pests away from trees that produce fruit for sale.
“I love dreaming,” Garczynski said. “I try to keep myself open to almost anything.”